Bug#1067577: sysprof: B-D on libunwind-dev which is not generally available

[Jeremy Bícha]

> So the best that is likely to be possible in src:sysprof without libunwind
> is to compile only libsysprof-capture, and not libsysprof or the sysprof
> application. I'm not convinced that would actually be practically useful -
> if libsysprof-capture is available but libsysprof isn't, then the library
> or application will be reporting better context/traceability about where
> it's spending its time, but nothing will be reading that information,
> making it seem somewhat pointless.

When this was written, I agreed. However, I am now leaning the other
way. There are 15 packages with Build-Depends:
libsysprof-capture-4-dev (a 16th, mutter needs more of sysprof). It
takes a fair amount of time to update the architecture lists in
debian/control and debian/rules for all of these.

I specifically want to build libsysprof-capture-4-dev everywhere.
libsysprof will still require libunwind and the sysprof still requires
gtk4 and libsysprof.

Thank you,
Jeremy Bícha